The manufacturing of flexographic printing webs or flexographic printing plate precursors, that have photopolymerizable layers, for flexographic printing is a multi step process that produces a number of layers on a substrate in preparation for later steps that place images on the precursor. The flexographic printing plate precursors typically consist of a substrate suitable for flexographic printing with one or more photopolymerizable layers and optionally oxygen barrier layers. In the process a film or element in which a mask image can be formed that then can be used to form an imaged element bearing a relief image. These mask-forming films are readily useful for preparing flexographic printing plates, and to methods of making such plates.
Radiation-sensitive elements having a laser-ablatable mask layer on the surface are known in the art. A relief image can be produced in such elements without the use of a digital negative image or other imaged element or masking device. Films with a laser-ablatable mask layer can be formed by first imagewise exposing the film with laser radiation (generally an infrared radiation laser under computer control) to selectively remove the mask layer in the exposed areas. The masking film is then placed in contact with a radiation-sensitive element and subjected to overall exposure with actinic radiation (for example, UV radiation) to cure the radiation sensitive element in the unmasked areas and thus form a negative image of the mask in the element. The film containing the mask layer and the imaged radiation-sensitive element (such as an imaged printing plate precursor) are then subjected to solvent development. The unexposed printing plate areas and the mask layer are completely developed off, and after drying, the resulting imaged element is useful, for example as a flexographic printing plate.
While flexographic printing plates having an integral laser-ablatable mask layer allow direct imagewise exposure using a laser and do not require a separate masking device, the time for imaging is generally too long since the system sensitivity to imaging radiation is low. Various attempts have been made in the industry to overcome this problem by increasing the infrared sensitivity of the mask layer. However, obtaining higher sensitivity has been a challenge due to the widely varying quality criteria that must be simultaneously satisfied. In addition, this approach requires the use of high-powered laser-equipped imaging apparatus that is especially configured for imaging flexographic articles. Because of the need for varying the thickness of flexographic plates depending upon the specific intended uses, more than one imaging apparatus may be required for the integral-mask approach.
An important advance in the art of making and using masking films is described in a few publications owned by Eastman Kodak, including U.S. Patent Application Publication 2005/0227182 (Ali et al., hereinafter cited as US '182) which describes a method where a cover sheet is removed before exposure and Ser. No. 11/130,065 as well as application 93576 which discuss a method wherein the cover sheet is removed after exposure. The described methods provide various ways of making a mask image in significantly less time due to greater imaging sensitivity.
In a typical manufacturing line, the layers laid down on the substrate need to be protected during the process when the layers are tacky, for example during lamination or undesirable properties such as delays, non-uniformity and even unusable flexographic printing plate precursors will result.
These problems may be overcome by use of a specially designed apparatus and related method for laminating a masking film onto a pre-press flexographic printing plate to place the plate in optical contact by applying a balanced, non-distorting force to the flexographic printing plate and masking film.